The invention relates to aircraft flight control systems, and, more particularly to automatic throttle-position tracking apparatus for multiengine aircraft.
Existing autothrottle systems which are used to drive two or more throttles utilize a single servomotor driving a mechanical clutch arrangement, which in turn, drives the several throttles. The clutch drives all of the throttles universally and equally in response to the servomotor input; however, each of the throttles may also be manually driven independently of each of the other throttles in response to a separate input to the clutch from each of several throttle control levers or handles, which handles are manipulable by the pilot of the aircraft. Each of the inputs to the clutch from the throttle control handles overrides, individually, the universal input from the servomotor. The throttles may thus be controlled individually by the pilot, or in unison by a flight control system through the servomotor input to the clutch.
The aforedescribed system has the disadvantage of requiring that the clutch mechanism and servomotor be located in the throttle quadrant of the aircraft cockpit. Such mechanical clutches are bulky and cumbersome, making access thereto difficult in the less than spacious environment of an aircraft cockpit. Further, lengthy mechanical linkages between the servo and the engine throttle mechanisms tend to introduce backlash and dead zones into the control loop, thus degrading loop performance.
When the pilot overrides the servomotor input to the prior art clutch mechanism by manually operating the throttle control handles, it may become apparent to him through tactile sensation or other sensory indication that an anomaly exists in the autothrottle system, e.g., the servomotor input may immediately begin, incorrectly, to compensate for the pilot's manual adjustment of one or more of the throttles. Upon such awareness, the pilot would of course disengage the autothrottle system by actuating any one of several switches located conveniently, as for example, on an overhead control panel. The prior art autothrottle systems, because of the already crowded space around the throttle quadrant do not provide a disengage switch in the most convenient of locations, on the throttle handle itself.
When two or more rate servos are commanded together such as in a multiengine aircraft having an autothrottle system with a separate throttle servo for each engine, the servos will tend to drift and thus not maintain accurate positional relationship with respect to one another. Moreover, when commanded by the autothrottle system to advance or retard the throttles in synchronism, multiple servos also drift apart positionally with respect to one another because the integration rates are not precisely the same for all the servos. Since it is desirable to utilize rate servos in autothrottle applications, means must be provided for compensating for the aforementioned drift, thereby causing all the servos, and in turn the throttles and throttle handles, to act as if they were one. Otherwise stated, when the pilot manually positions the several throttle control handles to a desired positional alignment, each with respect to the others, and then activates the autothrottle mode of operation as by removing his hand from the throttle handles, the throttles must be advanced or retarded simultaneously and in unison by the servos in response to control signals from the autothrottle system, maintaining precisely the relative positional alignments originally established by the pilot.